Due to growing worldwide concerns about the proliferation and possible smuggling or other transport of radioactive nuclear materials across borders of states and countries, governments of several nations have recently requested and commissioned the installation of radioactivity monitors at a large number of international border crossing locations.
A design of one type of conventional radiation detection system (further referenced herein as radiation detection system type A) located at a border crossing point, such as a highway that intersects two adjoining countries, includes a respective dedicated pair of radiation detector assemblies positioned on each side of each lane of the highway. Each radiation detector assembly pair for each lane includes two Gamma radiation detectors that are shielded with a radiation shield on the backsides of both Gamma detectors (i.e., the sides of the Gamma detectors that face away from the lane which those detectors monitor) in order to shield the detectors from ambient or background radiation that may affect the accuracy of the detector in detecting a radiation source within the lane associated with those detectors. The shielding also minimizes the influence of radiation variations caused by vehicle induced shielding of the background radiation by vehicles in neighboring lanes that pass adjacent to a detector assembly. The shielding on the backsides of the detector pairs associated with a particular lane of the highway may be, for example, lead plates (typically 1 cm or less in thickness) or steel panels or other radiation absorbing materials disposed respectively upon each detector assembly.
Each lane in such a conventional system design thus requires two shielded radiation detectors dedicated specifically to detecting radiation sources within that lane. If two lanes are adjacent to one another, the two shielded detectors positioned between the adjacent lanes can be arranged in a back-to-back configuration such that the shielding of the two detectors faces each other. In an alternative conventional configuration, opposing shielded detectors positioned between adjacent lanes are arranged side-by-side such that the unshielded front side (i.e., the radiation detecting side) of one detector for one lane is parallel or flush with a shielded backside of the other detector for the other adjacent lane. The side-by-side configuration consumes somewhat less real estate in the cross-lane direction and is useful in situations where there is not much area to provide for installation of such systems. Regardless of the configuration, each lane in this conventional design requires the use of two separately shielded radiation detectors in order to adequately detect a radiation source within that lane.
The radiation detector pairs for each lane in a conventional system design are coupled to a controller device that receives radiation detection signals from the detectors in that lane in order to process such signals and, optionally, to notify a central computer system in the event that one or both detectors in any particular lane detect a radiation source traveling within that lane. The central computer system can be located, for example, within a tollbooth, border crossing or customs station located downstream from the traffic flow of the lane with respect to the radiation detection system. As an example, the radiation detection system may be placed 100 or more meters ahead of a border crossing station. In this manner, as a car, truck or other vehicle traveling in lane transports a radiation source through a detector pair associated with that lane, the radiation source within the vehicle activates one or both of the detectors for that lane. In response, the controller coupled to the activated detector can notify an operator directly or through the central computer system in order to stop the vehicle at the customs station or tollbooth for further inspection in order to determine the legitimacy of the radiation source being transported by the vehicle.
Another radiation detection system design (further referenced herein as radiation detection system type B) uses a single radiation detector disposed between adjacent lanes of a multilane highway. The outer lanes of the highway are flanked on each outer edge with a single detector as well. All of the single detectors in this alternative configuration are coupled to a common controller or central computer system that notifies an operator of the trafficking of radiation within the lanes in the event a vehicle carrying a radiation source passes one of the detectors.